As a consequence of that surgical procedures in the eye when replacing a defect natural lens have been more perfected and less traumatic, for example after the development of resilient lenses capable of being folded through a small incision in the eye, phakic intraocular lenses are increasingly conceivable as an alternative to correct for optical deficiencies besides spectacles and conventional contact lenses.
In a general sense phakic lenses can be considered for implantation, either in the anterior (front) chamber of the eye between the cornea and the iris, or in the posterior (rear) chamber located between the iris and the natural crystalline lens.
Phakic lenses positioned in the anterior chamber have been considered as desirable in several earlier embodiments for the reason that this chamber is considerably larger than the posterior chamber and thereby admitting a less complicated surgical process. However, these types of lenses show series of drawbacks essentially related with an irritation action from the support means (haptics) on the sensitive eye structures. For example, the support means can, when positioned in the corner between cornea and iris, disturb the aqueous outflow and consequently generate an increase in the intraocular pressure, a condition, which at worst may induce glaucoma. Pressure on the support means on the anterior chamber angle can disturb blood circulation and cause pupil ovalization. Further, the support means and the optic may come in contact with the corneal endothelium and cause endothelial dystrophy with resulting loss of corneal transparency. Alternatively, the support means have been suggested to be fixated directly to the iris by various attachment means. A negative consequence of iris fixation is irritation of the iris.
It is a general complication when designing IOLs to be implanted in the posterior chamber between the iris and the natural crystalline lens that the available space is small. Consequently, the lenses cannot be bulky as frequently is required when a high power optical correction is considered. In particular, consideration must be taken to avoid or restrict any contacts with the intact natural crystalline lens, in order to prevent it from damages, which may lead to local opacifications, or at worst case cataract formation.
Considerations must also be taken to that contact with iris could result in abrasive damages with resulting pigment dispersion and that the pupil must not be blocked, so the flow of aqueous humor is prevented which may lead to raised intraocular pressure and reduced circulation of nutrients and metabolites to and from the natural crystalline lens.
U.S. Pat. No. 4,585,456 (Blackmore) discloses an early version of a posterior chamber phakic IOL that is fixed in position by appendages that contact the ciliary sulcus. In the embodiments described herein no considerations have been taken to minimize contact with surrounding sensitive eye structures.
U.S. Pat. No. 4,769,035 (Kelman) also describes a method of correcting eyesight with an IOL positioned between the iris and the natural lens. The method involves a step of determining the shape of the natural lens in its flattest natural condition (i.e. non-accommodated) and forming a posterior surface of the IOL which has a curvature conforming with the natural lens in said condition. The resulting IOLs will be in permanent contact with the natural lens, which means that there will be a risk that damages are caused in its structure with cataract formation as a consequence.
To minimize the risk of contacting the natural lens several designs have been suggested where the lens is provided with supporting means to secure to the ciliary sulcus. U.S. Pat. No. 5,258,025 (Fedorov) relates to a correction IOL for implantation between the iris and the natural lens having modified supporting elements with a tapered peripheral part serving to protect the ocular tissues from such interaction with the lens that could result in postoperative inflammations.
European Patent 0 563 602 (Chiron Adatomed) discloses a correction lens for the posterior chamber of the eye provided with an outer haptic portion designed so as to distance the correction lens from the natural lens while enabling a securing contact with the zonule fibers of the ciliary sulcus in order to properly define the lens position. The geometric configuration of the correction lens and the presence of openings for fluid circulation in the haptics serve to provide for that the anterior surface of the natural lens remains accessible for the metabolic processes occurring at this location.
Fixating correction lenses in the ciliary sulcus is not preferred, because the sulcus has an irregular shape varying between different individuals and it will be difficult to accurately size the overall lens length. It will either be to short, or have an unpredictable central distance to the natural lens, which means that the optical correction cannot be sufficiently controlled. It is another disadvantage that the correction lens is in a fixed in a predetermined position when the pupil is off-center. Further, the force of the sulcus-fixated lens exerted on the ciliary tissues increases the risk of a blood/aqueous barrier break.
It has therefore been suggested to design correction lenses for the posterior chamber to float on a layer of aqueous humor in front of the natural lens, without having any permanent securing contact with the ciliary sulcus periphery and follow the movements of the pupil. The length of a free floating lens is smaller than the sulcus diameter and the lens will rest on the zonula or be pushed forwards by the aqueous humor secreted by the ciliary body. The aqueous flow can thereby more easily reach the entire surface of the lens and bring nutrients to the natural lens surface and remove derivatives from its metabolic process.
International Patent Applications published as WO 89/02252 (Mezhotraslevol Nauchno-Tekhnichesky Komplex “Microkhirurgia Glaza”) and WO 95/15733 (Voir Et Vivre) disclose floating corrective IOLs for the posterior chamber wherein the supporting elements (haptic part) of the lens are considerably smaller in diameter than the ciliary sulcus and the lenses are secured in a corrected position by iris contact from dilations of the pupil acting on the optical part which protrudes into the anterior chamber of the eye. These lenses suffer from the drawback from that their optical parts have a limited diameter and that the edge of the optical part can scatter light with the result of undesired formation of halo-shaped optical sensations.
U.S. Pat. No. 5,480,428 (Fedorov) discloses a floating posterior chamber correction lens with a protruding optical part centered by the iris. In order to enable fluid circulation, in case the pupil is blocked by the lens, the optical part is provided with a central hole thereby avoiding the need of creating a hole in the iris (iridotomy). Further, this lens has a positioning element with a posterior surface having a radius largely following that of the natural lens, which is larger than the radius of the posterior surface of the optical part. This design means that the lens will be bulky, especially if a high refractive outcome is desired, so that the lens may be pushed forwards and apply a force against the iris by the pressure exerted from accommodation of the natural lens. Permanent disturbances of the iris can at worst induce pigment dispersion followed by pigmentary glaucoma. There is also a risk that a permanent forward dislocation of the iris can lead to that the anterior chamber angle closes the trabecular meshwork involved in aqueous humor transportation. When this condition is permanent the intraocular pressure can be chronically raised.
U.S. Pat. No. 5,913,898 (Feingold) discloses a corrective lens for the posterior chamber of the eye provided with features on its anterior side that enables a more smooth contact with the iris so as to avoid damages of wear due to long term contact. This patent also discloses means for allowing sufficient circulation of eye fluids around the lens, so as to avoid the built up of pressure differences between the posterior and the anterior chambers of the eye.
WO 98/17205 (IVI) discloses a farther developed floating corrective lens for the posterior chamber wherein more considerations have been taken to the interaction with iris by making the lens thinner and having the optic part substantially in the posterior chamber. However, this lens design cannot avoid pupillary block of circulating fluids, so the need of applying iridotomies (holes in the iris) remains. Further, these lenses do not consider any precautionary means to avoid damages to the zonulas and to surface of the natural lens.
Even if efforts are made in the corrective lenses for the posterior chamber to avoid disturbing the highly sensitive natural lens and thereby risk to induce the formation of opaque areas or a cataract, there still is a need to develop a lens having a posterior surface that contributes to avoid or decrease the risk of inflicting damages to the natural lens or to the zonulas. As will become apparent in the below in the descriptive part and the objects of invention, the presently inventive lens aims to provide a solution to these problems.
It is an object of the present invention to provide a corrective lens having an improved adaptation to the free space available in the posterior chamber of the eye between the iris and the natural lens so as to avoid any disturbances to the natural tissues.
It is another object of the present invention to provide a corrective lens for the posterior chamber of the eye that minimizes the contacts with the natural lens so as to avoid the cataract formation.
It is a further object of the present invention to provide a corrective lens having a posterior surface facing the natural lens designed to avoid stress concentration in this region.
It is a still further object of the present invention to provide a corrective lens with supporting means, which are adapted so as to avoid inflicting damages to the zonulas or to the ciliary sulcus.
These and other objects of the invention, which will be described in more detail below, or will be obvious from later explanations, are met with the presently invented lenses as disclosed in the following descriptive sections.